Safety sheathed blasting explosive cartridge



July 4, 1950 J. TAYLOR EIAL SAFETY SHEATHED BLASTING EXPLOSIVE CARTRIDGEFiled Sept. 20, 1945 FIG.

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J G F 5 s mi T NO MUD mAm SH C E L A ATTORNEY Patented July 1950 UNITEsure SAFETY sans-man nrns'rmd EXPLOSIVE CARTRIDGE Britain ApplicationSeptember 20, 1945, Serial No. 617,695 In Great Britain November 15,1944 1 Claims. 1

The present invention relates to the provision of new or improved safetysheathed blasting explosive cartridges by which we mean a cartridge of adetonating explosive, made from a composition including a suitableproportion of ingredients adapted to minimise its capacity for ignitingflredamp air mixtures or coal dust air mixtures when it detonates, isfurther provided along its cylindrical surface with an external safetysheath that also comprises flame quenching or cooling ingredients. Moreparticularly the invention has reference to the composition of thesafety sheaths in such cartridges, and has for an object to providesafety sheathed blastin cartridges that can be more advantageouslymanufactured or are superior in service to the hitherto known cartridgesof the kind described.

In safety sheathed detonating explosive cartridges the explosivecomposition customarily includes ammonium nitrate as one of its powerproducing ingredients, and one or more. compounds capable ofvap'orisation, fusion, or thermal decomposition with absorption of heatas a flame quenching or coolin ingredient, and the safety sheath alsocomprises one or more compounds of the latter description. In thiscountry it is also the practice for the explosive cartridge proper to beprovided with aewaterproofed paper wrapper and for this portion of thesheathed cartridge to comply with the oflicial gallery tests forPermited Explosives.

The .blanketing efiect of carbon dioxide on the flame of the explosiveand its innocuous character render it a particularly desirable gas to begenerated by the sheathing material when the detonation takes place.Sheathing materials consisting essentially of various more or lessinsoluble metal carbonates have been tried with varying results. Of thecarbonates sodium bicarbonate is the most effective and is the compoundgenerally employed in practice in this country, notwithstanding the factthat it is slightly soluble in water and must .be carefully separated bya waterproof wrapping from the explosive cartridge, since it wouldotherwise react with the ammonium salt present in the explosive, toproduce ammonium bicarbonate which gives rise to loss of ammonia andcarbon dioxide.

We have now found that the'flame quenching or cooling efiiciency of themetallic carbonate is substantially increased or other advantages areobtained by employing the metallic carbonate in admixture with asuitable proportion of hydrated alumina.

According to the present invention the safety z sheath of a safetysheathed blasting explosive cartridge of the kind described comprises amixture of one molar part of a metal carbonate not freely soluble inwater and 0.33 to 2.0 molar parts of a dry hydrated form of alumina.

As alumina, even in hydrated condition, has little or no more effect asa safety sheathing ingredient than calcium carbonate, it is surprisingthat mixtures of a metallic carbonate and hydrated alumina in suitableproportions should be more effective than either ingredient, and theeffectiveness of such mixtures may be attributed to the ready occurrencewhen the cartridge detonates of a heat absorbing reaction between thecarbonate and hydrated alumina resulting in the formation of a metallicaluminate, water and carbon dioxide. In the case of a bicarbonate, suchas sodium bicarbonate, this reaction would further liberate more carbondioxide-than could be obtained from simple thermal decomposition of thebicarbonate. although such thermal decomposition occurs much morereadily in the case of normal carbonates.

While artificial forms of hydrated alumina, obtained by precipitationfrom aluminium salt solutions, may advantageously be used, there arealso available natural forms of hydrated alumina that can be easilybrought to a suitable state of division desirably free from grittiness.These can accordingly be applied for sheathing the cartridges withoutappreciable hazard of explosion resulting from friction, should for anyreason the separation of the explosive ingredients from the sheathingmaterial be incomplete. Such forms of natural hydrated alumina includefor instance amorphous natural hydrated alumina, bauxite and gibbsite.

As the metal carbonate not freely soluble in water there may be employedfor instance sodium bicarbonate. or a metal carbonate substantiallyinsoluble in water; and in the latter case naturally occurring formseither hydrated or anhydrous, are frequently available; thus com minutedlimestone, chalk, calcareous shell, dolomite, or magnesite, may be used.The metal'carbonate should not .be more soluble in water than sodiumbicarbonate.

The hydrated alumina and the metallic carbonate are advantageously bothused in a fine state of division. If desired, other flame quenchin orcooling ingredients may be added to the mixture in minor proportions.

The drawing illustrates three alternative methods of utilizing thisinvention. Figure 1 illustrates a shell having the explosive charge Ienclosed by a paramned paper wrapper 2, a second paper wrapper 4completely surrounding the wrapped charge, and the annular space 8between the two wrappers filled with the powder mixture of theinvention. Figure 2 illustrates a rigid cylindrical sheath 5 formed bybinding the powder mixture of .the invention with a binder such asplatser of Paris, theexplosive charge I being then loaded into thecylinder. Figure 3 illustrates an explosive charge I wrapped with aflexible sheet 6 made by incorporating a flexible binder with the powdermixture of hydrated alumina and metallic carbonate.

British Specification No. 416,586 discloses inter alia a flexible safetysheathing material for blasting explosives comprising in sheet form auniform mixture of a fibrous bonding material and a preponderatingproportion of a cooling salt or mixtures of cooling salts.

British Specification No. 424,784 discloses inter alia a method offorming materials suitable for use as cooling sheaths for safetyblasting explosives wherein one or more cooling salts are mixed into apaste with an aqueous solution of a suitable organic binding agent suchas gelatine and a hydroscopic polyhydric alcohol such as glycerine, thepaste formed into any desired shape and dried.

The invention is illustrated by the following example:

Example Waxed paper covered cartridges of overall diameter 1%"containing explosive Polar Dynobel No. 2 are held centrally in a papershell of 1 diameter closed 'in at one end. A mixture containing 61 percent of commercial trihydrate of alumina of which 99 per cent passes a100 mesh and 90 per cent passes a 150 mesh British Standard Sieve, and39 per cent of ground chalk, of which the whole passes a 150 meshBritish Standard Sieve is poured into the annulus between the waxedpaper cartridge and the outer paper shell. The mixture is consolidatedby tapping and the filling and tapping operations are repeated until thewhole length of the cartridge is embedded in the mixture, care beingtaken to prevent accumulation of the mixture on the ends of thecartridge. The weight of the flame quenching mixture amounts to 45 percent of the weight of the explosive.

A charge consisting of flve cartridges (30 em. in all) each containing 6oz. of Polar Dynobel No. 2 sheathed in the above manner fired suspendedfreely in a 9 per cent methane-air mixture did not cause an ignition ofthe gas when initiated by a No. 6 electric detonator. Under similarconditions, the same explosive unsheathed gave a gas ignition at 6 oz.and sheathed with either chalk alone or hydrated alumina alone gave gasignitions with 10 oz. charges.

4 The Polar Dynobel No. 2 contained:

Per Cent Nitrated mixture of glycerine and ethylene glycol (:20) 13.0Ammonium nitrate 67 Sodium chloride 12.5 Woodmeal 5.0 Paraflln wax 1.0China. clay 1.5

We claim:

1. A safety sheathed blasting explosive cartridge wherein the safetysheath comprises a mixture of one molar part of a metal carbonate notfreely soluble in water and 0.33 to 2.0 molar parts of a dry hydratedform of alumina.

2. A safety sheathed blasting explosive cartridge as claimed in claim 1wherein the dry hydrated form of alumina is an artificial form obtainedby precipitation from an aluminium salt solution.

3. A safety sheathed blasting explosive cartridge as claimed in claim 1wherein the dry hydrated form of alumina is a natural form brought to asuitable state of subdivision.

4. A safety sheathed blasting explosive cartridge as claimed in claim 1wherein the metal carbonate is sodium bicarbonate.

5. A safety sheathed blasting explosive cartridge as claimed in claim 1wherein the metal carbonate and dry hydrated form of alumina are in afine state of division.

6. A safety sheathed blasting explosive cartridge as claimed in claim 1.wherein the metal carbonate is calcium carbonate.

7. A safety sheathed blasting explosive cartridge as claimed in claim 1,wherein the metal carbonate is magnesium carbonate.

JAMES TAYLOR. ALEC HAROLD PHILLIPS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES United States Dept. ofAgriculture Circular No. 466, March 1938, A Weather-ResistantFireproofing Treatment for Cotton Fabrics" by M. Leatherman. Copy inDivision 38.

